USING STREAMBED TEMPERATURE TIME SERIES AND PUMPING TESTS TO CHARACTERIZE GROUNDWATER AND STREAM WATER INTERACTION IN NORTHERN MAINE

Groundwaters and surface waters are environmentally and economically significant resources that are intimately interconnected. Groundwater inflow influences steam ecosystems, including fish habitat, and this inflow may be impacted by local groundwater extraction. Balancing ecosystem needs for groundwater with human demands on aquifers requires a clear quantitative understanding of groundwater interaction with surface water. As a result, groundwater influx to B-stream (Houlton, Maine) is being quantified using temperature time series data. Time series of vertical temperature data from the streambed were collected at 10-minute intervals for 2-week periods, seven times through the summer of 2014. Two arrays of 24 data loggers were installed near the edge of B-Stream in a rectangular configuration to collect streambed temperature at depths of 0cm, 8cm, 16cm, and 24cm. Temperature oscillations decrease from 3-4^oC at the streambed to 0.5-1.0^oC at depths of 24cm. Vertical groundwater velocities were calculated using measured temperature data to calibrate a one-dimensional finite-difference heat transport model. Best fits were determined by minimizing the sum of squared temperature residuals while systematically adjusting vertical groundwater velocity and porosity used in each simulation. Vertical groundwater velocities were upward and ranged from 1e-5m/s to 3e-6m/s with normalized sum of squares averaging 0.220^oC and ranging from 0.163^oC to 0.296^oC. Hydraulic tests were conducted by pumping two bedrock wells located 10m and 35m from the edge of B-stream at rates of 2.8 to 5.7 liters/min. Cooper-Jacob analysis of the drawdown data yield transmissivity values ranging from 1.38e-6m²/s to 2.49e-6m²/s. In the next phase of this project, temperature time series data will be evaluated in greater detail to determine the impact of hydraulic tests on vertical groundwater flow rates.